The nicked circular DNA and the nicked DNA-protein complex have been isolated from Simian Virus 40. The nick may occur on either strand of the DNA and the nicks in the two strands are slightly staggered with respect to each other. A part of the nicked circular DNA possesses a protein covalently attached to the end of the single strand DNA and the protein maps at about 0.67 genome unit from ecoRI restriction site. We will extend this study further. The nicked DNA will be isolated from virus and cleaved with restriction endonucleases. The fragments containing nicks will be analyzed to determine the location of the nicks on both strands of viral DNA with the aid of cRNA made in vitro. The chemical state of terminal ends of the DNA at the nick will be studied with the aid of enzymes of DNA metabolism. The protein will be isolated from the purified protein-DNA complex and its molecular weight will be determined. Tryptic digest pattern of the protein will be compared with viral polypeptides and amino acid analysis of the protein will be carried out. The nicking ability and the protein-DNA complex forming ability will be examined in the virus of various SV40 temperature sensitive mutants at non-permissive temperature. Several distinct minor polypeptides have been observed from lysates of highly purified virus. Minor polypeptides will be purified from virus and characterized to determine their molecular weight, the number of copies of each per virion, their origin and their relatedness to other viral polypeptides. A detailed understanding of these minor and essential polypeptides contained in virus and protein-DNA complex formation is important for the understanding of the growth of the virus and of malignant transformation.